1. Field
Example embodiments relate to analog digital converters (ADCs), for example, ADCs capable of performing bi-directional integration and image sensors including the same.
2. Description of the Conventional Art
Conventional image sensors are classified as charge coupled device (CCD) image sensors or complimentary metal-oxide semiconductor (CMOS) image sensors (CISs). Compared to CCDs, conventional CISs are more economical because they use a general CMOS process. Conventional CISs are also more advantageous with regard to integration because conventional CISs can be integrated with an analog/digital signal processing circuit. In addition, conventional CISs may operate with relatively low power and relatively low voltage. As a result, conventional CISs are used more widely in portable apparatuses such as mobile phones, digital cameras, and the like.
A pixel array of a conventional CIS includes a plurality of pixels arranged in a two-dimensional matrix. Each of the pixels outputs an image signal corresponding to optical energy. In more detail, each of the pixels includes a photodiode that integrates photo charges corresponding to the amount of incident light and generates an analog pixel signal on the basis of the integrated photo charges. An ADC converts the analog pixel signal output from each of the pixels into a digital pixel signal, and an image signal processor (ISP) image processes pixel data corresponding to the digital pixel signal.
A conventional sigma-delta ADC, usable during analog-digital conversion, converts an analog pixel signal into a sigma-delta 1-bit digital bitstream through sigma-delta modulation, and obtains multi-bit digital data corresponding to the analog pixel signal from the sigma-delta 1-bit digital bitstream. However, when the conventional sigma-delta ADC performs two analog-digital conversion operations, overhead to post-process results of the two analog-digital conversion operations exists. Conventionally, a method of bitwise inverting a result of one analog-digital conversion operation has been used to reduce the overhead time. However, this method causes relatively high current to flow in the conventional sigma-delta ADC.